The present invention relates to gas turbine controls and more particularly to gas turbine startup speed monitors.
In the operation of a power plant gas turbine, there are certain relatively narrow critical speed ranges where resonant conditions occur and costly stress damage or failure of blades and other parts can occur if the turbine is operated at those speeds for even relatively brief periods of time. Although turbine startup normally calls for smooth and continuous increasing speed from ignition to synchronism, the turbine may develop some problem or other circumstances may arise which cause the turbine temperature limit or surge control to hold the turbine at a particular speed for some time.
Protection has conventionally been provided against turbine operation at resonant speeds by the use of a plurality of sequence timers which cause the turbine to trip if the turbine fails to reach a designated higher speed from a designated lower speed within a preset time period measured by the timer associated with that part of the startup sequence. One difficulty with the sequence-timer approach is that the turbine may reach and operate at a critical speed during most of the measured time period, thereby creating the possibility that significant stress damage or part failure will occur before the turbine is signalled to trip by the timer.